eight: the cardinal number, one more than seven
This is simply the number eight, used the way any number is used: counting people, days, years, objects, and measurements. It appears in census totals, the ages of kings, the dimensions of the tabernacle and temple, and the lengths of reigns and captivities. There is nothing hidden in the word itself, and there is no second meaning to tease out: it counts, and it counts to eight.
Where eight gains weight in the Bible is not in the word but in a few of the settings it keeps. A boy was circumcised on the eighth day, the day after a full week of life had passed, marking him as a member of the covenant people. Several offerings and dedications also reached completion on an eighth day, after a seven-day span. Because seven so often stands for a finished cycle, the eighth day reads as the morning after that cycle, a fresh start on the far side of completeness.
One famous count is the eight people carried safely through the flood in the ark: Noah, his wife, his three sons, and their wives. Later writers looked back on that small number as the seed of a renewed world. None of this changes what the word means. Eight stays eight; the significance lives in what is being counted and when, not in the number itself.